Catalysts are employed on automobiles to treat engine exhaust gases to convert unburned hydrocarbons and carbon monoxide to carbon dioxide and water and to convert nitrogen oxides to nitrogen and water. Typically the catalysts comprise one or more noble metals such as platinum, palladium and rhodium in an extremely fine dispersion on a high surface area material such as gamma alumina. Such high surface area carrier may be in the form of an alumina pellet. In this case, the exhaust gas treatment is effected by retaining a bed of pellets in a suitable metal container which is shaped to direct the exhaust gas through the bed. In another arrangement, an extruded monolithic ceramic body is formed containing a large number of longitudinal open ended passages. The body is of a refractory material such as cordierite. In this arrangement, the noble metal is dispersed on an alumina washcoat which in turn is carried by the cordierite body.
It is known that certain elements such as lead or phosphorus if allowed to accumulate on the surface of the catalyst will drastically reduce its ability (activity) to treat the exhaust gas as intended. For this reason, there are restrictions on the amount of lead or phosphorus that are added to engine fuels. However, phosphorus is still employed in lubricating oils. When oil is consumed in the engine, phosphorus can be deposited on the surface of the catalyst, inhibiting its activity. The exact chemical form of the deposited phosphorus may not be known. It is likely that the major phosphorus-containing poisons, in the absence of significant amounts of lead, consist of complex mixtures of metal phosphates and hydroxyphosphates in varying degrees of hydration and crystallinity. These phosphorus-containing materials seem to glaze over the surface of the catalyst, preventing the noble metal from interacting with the exhaust gas.
It is an object of our invention to provide a simple method of rejuvenating a phosphorus poisoned automotive exhaust treatment catalyst. It is a further object of the invention to provide such a method of treating and rejuvenating a phosphorus poisoned catalyst with a suitable acid solution that could be carried out by a mechanic in a garage.